The present invention is related to the field of bath systems for processing semiconductor wafers and, more particularly, bath systems using sonic energy for processing such wafers.
In the present bath systems, a container is loaded with a cassette of semiconductor wafers and a processing liquid is pumped and filtered for recirculation through the container. Processing liquids can be powerful solvents used for chemical actions on the wafer surfaces; on the other hand, simple distilled water may be used as the processing liquid for rinsing operations.
A development in semiconductor bath systems has been the use of sonic energy which is directed against the wafers in the processing liquid. The sonic energy has been found to not only deliver kinetic energy for mechanically "scrubbing" the surfaces of the wafers, but also to help with the desired chemical reaction at the wafer surface/processing liquid interface.
However, bath systems using such sonic energy have not had optimal performance. In some systems, the sonic transducers have been mounted on the outside of the processing container with inefficient and uneven delivery of sonic energy to the wafers. To counter this problem, other systems have placed the sonic transducers on the inside of the processing container thereby exposing the transducers and their electrical connections to the sometimes corrosive properties of the processing liquid. This has sometimes lead to the contamination of the wafers.
Furthermore, such systems have not been able to operate at higher temperatures from the failure of the bonding used to mount the transducers at those temperatures.
Other problems with sonic bath systems have been that energy propagation at different sonic wavelengths, or frequencies, were not accounted for. Such disregard often leaves "dead spots" at which the wafers are not completely exposed to the action of the sonic energy. Conversely, some sonic bath systems operate without any obvious dead spots, but at energies which are not efficient for maximum throughput of the wafers through the semiconductor fabrication facility.
Costs are always of concern in semiconductor production. Typically in a semiconductor fabrication area, there are several bath systems, each of which contains different liquids for processing the semiconductor wafers. The different liquids may include water with varying degrees of chemical contamination for sequentially rinsing the wafers after a processing step. Associated with these bath systems are the purchasing costs for several systems for each fabrication area, and the costs of the processing liquids for the bath systems. There are also the costs associated with the handling of the wafers as they are moved from one bath to another, i.e., the time consumed in moving the wafers and the losses which inevitably occur in handling the wafers.
To overcome these problems, the present invention provides for a bath system in which sonic energy is delivered efficiently and wafer processing time is minimized.